Love is grand. But commitment? That’s kind of terrifying. And it’s not something movies typically dwell on, preferring instead to document the thrill of the chase rather than the complexities of the capture. A smart storyteller, however, understands that few things lend themselves to dramatic conflict better than the shoehorning of two free wills into one shared journey, especially when that unexpected third soul inevitably shows up and throws a wrench in the works. That’s the premise of “Take This Waltz,” a bittersweet, wisely observed film from Canadian filmmaker Sarah Polley (2006’s Oscar-nominated “Away From Her”), which watches as a young woman in a comfortable marriage finds herself drawn to an inconvenient man.

Michelle Williams (“My Week With Marilyn”) totally de-glams as Margot, who we first meet through a gorgeously golden opening scene in which the simple process of making blueberry muffins affords us a little window into the careful, seemingly impatient woman with blue toenails. The man who enters the shot is kept deliberately hazy, and the film flashes back to Margot’s meet-cute with Daniel (Luke Kirby), who yells, “Put your back into it” when the mortified Margot is tapped to flog an 18th-century scofflaw at the historical park. They encounter each other again on the plane; the able-bodied Margot arrived at the boarding gate in a wheelchair, and she confides to Daniel her fear of missed connections: “I don’t like being in between things.”

With that heavy-handed and symbolic foreshadowing business out of the way, we’re better able to appreciate the chemistry between the two, who discover upon parting that they’re neighbors. And when Margot returns home to her distracted cookbook-author husband, Lou (an excellent Seth Rogen), both the good and bad traits of their relationship come into sharp focus. Roughly 99 percent of the audience will nod/squirm in empathy with the ongoing jokes to the sweetly weird baby talk to the unmistakable sibling vibe that has settled over their five-year marriage. It’s no wonder she makes a concerted effort to seek out the darkly intense Daniel, who clearly wants to be found. The combination of Daniel’s pull, Lou’s push, and Margot’s own evolving boundaries culminate in the most scorching no-flesh/all-talk seduction in forever.

So does Margot run off with Daniel or is he merely a way for her to appreciate what she already has with Lou? This conundrum, the stuff of a billion cinematic love triangles, is where Polley’s truthful script is at its most perceptive. None of the parties get let off the hook for their actions (or inactions), each taking turns in the roles of both perpetrator and victim. “New things get old,” the naked stranger reminds Margot and her friends in that remarkable, unflinching scene in the showers, one that maybe only could have been filmed with a woman behind the camera. If there’s a quibble here, it’s that Polley’s throwaway details are perhaps a bit too contrived; these three people lead the most precious hipster existences.

It’s also not totally obvious why Daniel would set his cap toward Margot, but attraction isn’t always explainable. As played by the peerless Williams, Margot seems very real, a passionate, frustrated, and selfish human being with no safe place to direct all that churning emotion. Williams is well matched by her male counterparts, as Rogen delivers a career-best performance (admittedly, that bar is low-ish) and Kirby breathes honest life into a character that may be more archetype than actuality. Sarah Silverman steals her scenes as Lou’s wry sister Geraldine, a recovering alcoholic who understands Margot’s plight but opted for a different form of escapism. “Take This Waltz” is also dazzling in its vivid, color-drenched cinematography, with Toronto playing its underappreciated self in a wistful summer glow.